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Implement strStr().
Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Example 1:
Input: haystack = "hello", needle = "ll" Output: 2
Example 2:
Input: haystack = "aaaaa", needle = "bba" Output: -1
Clarification:
What should we return when needle
is an empty string? This is a great question to ask during an interview.
For the purpose of this problem, we will return 0 when needle
is an empty string. This is consistent to C's strstr() and Java's indexOf().
考察:字符串查找子串,类似于string类的find()函数,复杂点的可以用字符串匹配kmp;
class Solution {
public:
int strStr(string haystack, string needle) {
if(needle == "")
return 0;
//return haystack.find(needle);
int m = haystack.length(), n = needle.length();
if (m < n)
return -1;
for (int i = 0; i <= m-n; i ++) {
int j = 0;
for (j = 0; j < n; j ++)
if (haystack[i+j] != needle[j])
break;
if (j == n)
return i;
}
return -1;
}
};